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From Jun Rao <...@confluent.io>
Subject Re: Segments being deleted too early after upgrading 0.9.0.1 to 0.10.1.0
Date Tue, 01 Nov 2016 16:17:11 GMT
Hi, James,

That's a good point. KAFKA-3802 should cause the log segments to be kept
longer, instead of shorter. So, there is probably something else that's
causing this behavior. Could you try if you can reproduce this? When you do
that, one thing you could try is to set log.segment.delete.delay.ms to a
larger value. This will leave those segments to be deleted as .deleted
files longer. Then, when deletion is triggered, you can check the last
modified time of those .delete files and run the following command to check
the content of the .timeindex file. The content in the .timeindex file
should be empty, which means log retention will be using the last modified
time.

bin/kafka-run-class.sh kafka.tools.DumpLogSegments --files
/tmp/kafka-logs/test-0/00000000000000000000.timeindex

Thanks,

Jun

On Mon, Oct 31, 2016 at 5:17 PM, James Brown <jbrown@easypost.com> wrote:

> KAFKA-3802 does seem plausible; I had to restart the brokers again after
> the 0.10.1.0 upgrade to change some JVM settings; maybe that touched the
> mtime on the files? Not sure why that would make them *more* likely to be
> deleted, though, since their mtime should've gone into the future, not into
> the past...
>
> On Mon, Oct 31, 2016 at 5:02 PM, Jun Rao <jun@confluent.io> wrote:
>
> > Hi, James,
> >
> > Thanks for testing and reporting this. What you observed is actually not
> > the expected behavior in 0.10.1 based on the design. The way that
> retention
> > works in 0.10.1 is that if a log segment has at least one message with a
> > timestamp, we will use the largest timestamp in that segment to determine
> > if the segment should be retained. If no message in a segment has a
> > timestamp (which is your case), we will fall back to use the last
> modified
> > time of the segment, which is the old behavior.
> >
> > I tested this locally and didn't see old log segments being deleted
> > immediately after upgrade. It's also a bit weird that you only saw that
> in
> > the leader broker. The retention logic is orthogonal to a replica being a
> > leader or a follower.
> >
> > I am wondering if you could be hitting
> > https://issues.apache.org/jira/browse/KAFKA-3802 ? If not, is there a
> way
> > to reproduce this reliably?
> >
> > Jun
> >
> > On Mon, Oct 31, 2016 at 4:14 PM, James Brown <jbrown@easypost.com>
> wrote:
> >
> > > I just finished upgrading our main production cluster to 0.10.1.0 (from
> > > 0.9.0.1) with an on-line rolling upgrade, and I noticed something
> > strange —
> > > the leader for one of our big partitions just decided to expire all of
> > the
> > > logs from before the upgrade. I have log.retention.hours set to 336 in
> my
> > > config, and the replicas still have data going back to October 17, but
> > > after restarting for 0.10.1.0, the topic leader deleted all segments
> more
> > > than a couple of hours old (approximately 2TB of data on that box).
> > >
> > > inter.broker.protocol.version and log.message.format.version are both
> > still
> > > set to 0.9.0.1 in my config
> > >
> > > Before the upgrade, the oldest available offset in this topic/partition
> > > was 812555925; now it's 848947551.
> > >
> > > I assume this is some bug with upgrading to 0.10.1.0 when the extant
> data
> > > doesn't have any associated timestamps, but it seems, uh, really
> > > unexpected, and if I'd had any consumers which were behind, I could've
> > > ended up losing quite a lot of data here. It's particularly bizarre
> that
> > > this didn't affect anything except the leader (yet).
> > >
> > > It may be that this is expected behavior, but I guess I just assumed
> that
> > > the code would fall back to using the mtime if timestamps were not
> > present
> > > in the log rather than assuming that the timestamp of a given segment
> was
> > > 0. If this is expected behavior, I would recommend adding a specific
> note
> > > the the "Potential breaking changes in 0.10.1.0" section of the manual
> > > indicating that upgrading from 0.9.0.1 might immediately truncate all
> of
> > > your data.
> > >
> > >
> > > Debugging output is below:
> > >
> > >
> > > % kafka-topics.sh --zookeeper localhost:40169 --describe  --topic
> > > easypost.request_log
> > > Topic:easypost.request_log PartitionCount:4 ReplicationFactor:3
> Configs:
> > > Topic: easypost.request_log Partition: 0 Leader: 1 Replicas: 1,4,2 Isr:
> > > 4,2,1
> > > Topic: easypost.request_log Partition: 1 Leader: 4 Replicas: 4,1,2 Isr:
> > > 4,2,1
> > > Topic: easypost.request_log Partition: 2 Leader: 5 Replicas: 5,2,3 Isr:
> > > 5,3,2
> > > Topic: easypost.request_log Partition: 3 Leader: 3 Replicas: 3,5,2 Isr:
> > > 5,3,2
> > >
> > > ​(on broker #1):
> > >
> > > % ls -l /srv/var/kafka/logs/easypost.request_log-0/ | wc -l
> > > 25
> > >
> > > (on broker #4):
> > >
> > > % ls -l /srv/var/kafka/logs/easypost.request_log-0/ | wc -l
> > > 3391
> > >
> > >
> > > When the actual deletion occurred, there were no errors in the log;
> just
> > a
> > > lot messages like
> > >
> > > INFO Scheduling log segment 811849601 for log easypost.request_log-0
> for
> > > deletion. (kafka.log.Log)
> > >
> > >
> > > ​I suspect it's too late to un-do anything related to this, and I don't
> > > actually think any of our consumers were relying on this data, but I
> > > figured I'd send along this report and see if anybody else has seen
> > > behavior like this.
> > >
> > > Thanks,​
> > > --
> > > James Brown
> > > Engineer
> > >
> >
>
>
>
> --
> James Brown
> Engineer
>

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